1. Field of the Invention
The present invention relates to a brightness enhancement film having curved prism units. More particularly, the present invention relates to a brightness enhancement film having curved prism units each of which is extended in a meandering line to provide changes in curvature. The brightness enhancement film is applied to a Liquid Crystal Display that improves the entire optical refractive characteristic.
2. Description of the Related Art
Referring to FIG. 1, International Patent Publication No. WO 96/23649 discloses a brightness enhancement film including a base 1 and a plurality of prisms 2 juxtaposed in order on the base 1. Each of the prisms 2 consisted of a first flat facet 2a and a second flat facet 2b adapted to refract light to condense light.
However, the first flat facet 2a and the second flat facet 2b are flat surfaces different from curved surfaces and thus only able to refract light in one dimension with respect to a top horizontal surface of the brightness enhancement film. Namely, the brightness enhancement film is only able to condense light in one dimension as well as one-dimensional refraction.
Referring to FIGS. 2 and 3, U.S. Pat. No. 6,277,471, issued on Aug. 21, 2001 to Tang, discloses an another brightness enhancement film including a base 11 and a brightness layer 12. The base 11 has a top surface and a bottom surface. Also, the brightness layer 12 has a top surface and a bottom surface. A plurality of rippled ridges 121 are juxtaposed in order and each of which consists of brightness units 122 arranged in order. Each of the brightness units 122 consists of a pair of curved surfaces 123 and 214 which may refract light in two dimensions so that the brightness unit 122 is able to condense light in two dimensions. Structurally, the bottom surface of the brightness layer 12 is connected to the top surface of the base 11 to form the construction of the brightness enhancement film.
Referring again to FIGS. 1 and 2, U.S. Pat. No. 6,277,471 achieves condensing light in two dimensions by replacing the flat facets 2a and 2b of the prisms 2 disclosed in WO 96/23649 with the curved surfaces of brightness units 122. Therefore, U.S. Pat. No. 6,277,471 improves drawback of WO 96/23649 that merely condenses light in one dimension.
Referring again to FIG. 3, the brightness unit 122 consists of a first curved surface 123 and a second curved surface 124 whose curvature is able to refract light in two dimensions to accomplish the condensing function. The first curved surface 123 and the second curved surface 124 slope gently toward the top surface of the brightness layer 12 so that bottom edges of the first curved surface 123 and the second curved surface 124 are commonly terminated at a straight bottom edge 125. The straight bottom edge 125 is located between the two adjacent brightness units 122 and the straight bottom edges 125 are serially connected to each other to form a wave trough.
Generally, the curvature of the first curved surface 123 and the second curved surface 124 are able to refract light for condensing. However, the first curved surface 123 and the second curved surface 124 are sloped gently toward the straight bottom edge 125, and thus the surface adjacent to the straight bottom edge 125 is nearly a horizontally flat surface. The slight curvature of the flat surface is inadequate to refract light in two dimensions. Although the first curved surface 123 and the second curved surface 124 are able to refract light in two dimensions, the surface adjacent to the straight bottom edge 125 may reduce the entire refractive efficiency for the brightness unit 122 and cause a moire phenomenon.
Additionally, the structure of the brightness unit 122 is complicated and increases the manufacture cost of a mold assembly.
The present invention intends to provide a brightness enhancement film having curved prism units. Each of the curved prism units extends in a meandering line so that at least one surface of the curved prism unit provides changes in curvature, i.e., such that a direction of said meandering surface relative to said longitudinal direction varies along a length of each of said prism units. Thereby, the changes of the curved prism unit in curvature refract light in two dimensions to attenuate the moire phenomenon and the structure of the curved prism units is simplified in such a way as to mitigate and overcome the above problem.